Mark Mason of the O.S.S. and the Blonde Phantom are interrogating a man responsible for stealing international trade secret. When they press him to reveal who he is working for the man is tight lipped. As they leave the interrogation, Mark and Blonde Phantom talk about who they are certain is the mastermind: Senior Korte, a diplomat who they cannot touch without solid evidence due to his diplomatic immunity. Blonde Phantom abruptly departs when Mark offers to give her a ride home, and she wonders silently why Mark does not notice her in her civilian guise, Louise Grant, his secretary.

Meanwhile, Senior Korte meets with Senator Mushbell about the most recent capture of some of his men. However, despite the interference of the Blonde Phantom, Korte is certain that he will be able to get information from the secret atomic energy conference being held that Tuesday and begins detailing his plans to Mushbell.

That Tuesday, at the office of Mark Mason, Mason tells Louise that he suspects that something will happen at the atomic energy conference. Mark decides that he has been working too hard and decides to go out but wishes he could contact the Blonde Phantom to ask her out on a date. With no other options, he asks Louise to go out with him, much to her pleasure. As Louise gets ready, their assistant Willie questions why she is chasing after their boss when he clearly is in love with the Blonde Phantom. Smiling Louise says that maybe he can love both women.

Before they can leave for their date, Mark is visited by Gloria Bascom who has brought her cousin Professor Homer Johns an atomic scientist who was part of the conference earlier that day. Gloria asks Mark to accompany them to a party at Walter Edgar's estate and says that many rich and powerful people will be there, including Signor Korte. Hoping he can learn more about his foe, Mark agrees to go, brushing off his date with Louise. However, Louise is not disappointed, as it gives her an opportunity to show up at the party as the Blonde Phantom.

At the party as Mark shares small talk with Senior Korte, the Blonde Phantom arrives at the party. Suddenly, Homer keels over, a doctor checks him and declaring him dead of a heart attack and has an ambulance called. As the ambulance takes away Homer's body, Mark comforts Gloria while the Blonde Phantom examines the glass Home was drinking from and finds that it has a trace scent of poison. When investigating the doctor, they learn that he does not work at the hospital and nobody called in the emergency. Korte then mockingly gives Mark his condolences and hopes that whoever is responsible for killing Homer is caught before departing, pleased that his plan is going well. Gloria faints, and Mark leaves to bring her home, convinced that she was not involved in her cousins murder. However, the Blonde Phantom is not convinced as she finds part of a smashed vial that fell out of Gloria's purse that she believes contained the lethal dose of poison that killed Homer.

The Blonde Phantom then rushes to Gloria's house and as she searches for clues she hears two men snooping around and hides in the closet. However, they notice the marks made by her high heels on the carpet and find her. She tries to fight them, but is easily knocked out, just as Gloria and Mark arrive. The men quickly grab the paperwork they are looking for, stash the Blonde Phantom into a closet and escape out the window. Coming around, Blonde Phantom hears Mark and Gloria entering the house and purposely moans to take Mark's attention to Gloria back to her, much to Gloria's chagrin. Fully recovered, the Blonde Phantom explains what happens and accuses Gloria of being involved in the plot, but Gloria denies it, telling them that the smashed vial contained perfume. Although Mark knows that the Blonde Phantom has never been wrong before, he is pressured to believe Gloria's explanation. Soon the authorities call on Mark, telling him that he body of Homer Johns was found washed up on shore along the Potomac River and says he'll be right down.

Meanwhile, at Senior Korte's residence, he meets once more with Senator Mushbell and they gloat over how well their plan is working and that the atomic secrets are now theirs. He checks with his thugs who confirm that they got the paperwork from Gloria's house despite the interference from the Blonde Phantom, learning that they failed to kill her, he orders them to keep an eye on the heroine. At Mark's office, the Blonde Phantom learns that an autopsy was done on Johns' body, and that there was no trace of poison or undigested food in his system. As Mark leaves to confer with the chief of police, the Blonde Phantom recalls that she saw Mark eating at the party, and recalls overhearing the thugs that attack her mention that Homer was drugged and drowned under "heavy water". She leaves a note for Mark telling him to have the coroner examine the water in Homer's longs to see if it is river water.

Just then, the thugs burst in to stop Blonde Phantom from leaving the note. Holding her at gun point, the Blonde Phantom attempts to escape by dousing the lights, however her dress gets caught on an exposed nail and she is tripped up and captured. The crooks take the Blonde Phantom to a cabin in the woods where she finds that the masterminds are Walter Edgar, and "Homer Johns" who reveals himself to be really an impersonator and posed as Johns' after they killed him and memorized information at the atomic energy convention in order to sell the secrets. When Blonde Phantom presses them to reveal their leader, Edgar tells her that their employers identity is unknown, and that they communicate through short wave and leave information in an abandoned letter box.

Just then, Mark Mason and members of the O.S.S. suddenly burst into the room with guns trained and capture the gang before they can kill Blonde Phantom. Mark explains that he found a carbon copy of her note and was able to pinpoint the water in Johns' lungs to the lake water that feeds into the pipes at the house and were able to track her down. Later, with the paperwork recovered from the scene of the crime, Mark learns that Gloria was involved in the plot and has her arrested. Back at his office, Mark tells Louise that their trap set for the mastermind failed to net a capture. While at the home of Senior Korte, Korte plots revenge against the Blonde Phantom and Mark Mason.

At the home of millionaire stamp collector Jackson Cartwright, Cartwright is spending a quiet evening placing his newly purchased stamps in his stamp book when somebody stabs him to death. Passing by are Mr. Wu and his sidekick Alfie who hears cries for help coming from the Cartwright home and go to investigate. There they find Cartwright's son-in-law George Willis fighting with Smiley, the Cartwright butler. They both claim to have found the murdered Cartwright and fled the house, bumping into each other and starting the fight.

Mr. Wu and Alfie are allowed into the home to investigate the crime scene. Forcing their way into the study, Mr. Wu examines Cartwright's den, noting that the stamps he was placing in a book was a series of six, but one of the stamps is missing. Recalling that the butler mentioned that Cartwright's lawyer Mr. Evans was also in the house they decide to go and question him. As they make their way they hear a scream and rush to Evans' room. Alfie rushes in and seemingly chases of Evan's attacker, but it turns out to be Evans himself, who tells them his attacker escaped. He leads them to where the attacker went and they catch Smiley as he is preparing coffee, Alfie doesn't trust him.

However, Mr. Wu continues to question Evans and learn that Cartwright kept his important papers in a secret drawer in his study. Rushing there they catch Smiley snooping around and jump him. He admits he is looking for the will to insure that he is still entitled to his $5000 legacy. Mr. Wu finds the will and before they can do anything somebody throws a knife at them and misses striking Alfie. They rush after the attacker and find that it is Evans, who admits to killing Cartwright after forging the will so that he would receive $50,000 dollars from the estate. Mr. Wu reveals that he knew Evan's was a killer, pointing out that the missing stamp was stuck to the bottom of his shoe.

Madeline Joyce is spending time in her apartment reading back issues of the newspaper, researching a string of "accidental" deaths of young newly wed brides. She then gets a telegram from her cousin Mona who announces that she just recently got married and that she and her new husband will be coming by that afternoon.

Before her guests arrive, Madeline changes into Miss America to check with the police about the newly wed murders. Looking at the reports, she notes that while the husband's in all the deaths do not look alike, but all photos of the husband are left sided profile shots. With 2:00 approaching, Miss America rushes back to her apartment to meet with her cousin Mona in her civilian identity.

When Mona arrives she introduces him to her husband Merrill, who points out that he has an unusual eye. Mona's husband angrily strikes her and Madeline scolds him for hitting his wife. The man shows that his right eye has a square pupal due to an operation. He then suddenly leaves to buy cigarettes leaving the two women alone to talk. Mona admits to Madeline that her husband has never struck her before and has been so kind to her since her father died and that he used to be an actor. This raises Madeline's suspicions and when carrying their luggage into the spare room she notes that the initials on Merrill's suit case are "R.L." and recalls how the police reports listed one of the husbands was named Roger Lawton.

Madeline then takes her suspicions to Mona and suggests that Mona hide while she disguises herself as Mona. However, when Merrill returns, some of Madeline's hair is poking out of her blonde wig, revealing her true identity to Merrill and quickly chloroforms her. He takes her out to a cemetery and buries her alive. Having recovered, Madeline changes back into Miss America and bursts free. Meanwhile, Merrill has returned to the apartment and knocked out Mona and set her car speeding off a ship bridge while it is raised in order to collect Mona's family fortune. Miss America saves Mona, and as she chases Merrill, he runs off the bridge and falls to his death.

The Blonde Phantom has just finished helping the authorities capture the last member of an espionage ring. Returning to her home, she gets a call from Mark Mason, who asks her alter ego Louise to pack a bag as they are going to a special O.S.S. assignment in South America. Changing back into Louise Grant, the Blonde Phantom meets with Mark Mason at the air port. There he tells her that they are going to hunt down escaped Nazi Hans Rheint, who created a deadly formula during the war, and escaped when the Nazis lost the war. Their only lead is that they have located his wife Freyda who has been located in South America.

A day later, Freyda is wondering about a red scorpion as the O.S.S. agents pay her a visit. They explain why they have come to see her, and she cooperates, telling them that she hated her husband's Nazi ways and explains that he had died shortly after they arrived in South America. She tells them that after Hans died, a box arrived with a note from him, telling them that there are two red scorpions in the box, and that the second one will hold the secret of his formula. However, she explains that the box only contained a single red scorpion. As they explain this, they are unaware that Freyda's butler Carlos is listening through the keyhole. When Mark asks to check out Fredya's associates, she invites Mark and Louise to the party. However, that night, Louise calls Mark and feigns feeling sick so that she can attend the party as the Blonde Phantom.

The Blonde Phantom arrives at the party and uses her feminine charm to try and get a feel for the party goers. One man named Alfredo pays the most attention to her and while they are out getting fresh air he tells her to come to his home some day to see his large record collection. As she flirts with the various guests she tells them that they found the second red scorpion to see if they can draw out who might actually have it. She soon leaves with Mark and tells him the plan, they soon find that they are being tailed. Stopping they beat their tail into submission, but before he can tell them who he works for somebody shoots him dead. Mark is also wounded in the drive by shooting. Searching the dead man's body, they find a number of phonograph needles in his pocket.

After the Blonde Phantom brings Mark to the hospital and then decides to pay a visit to Alfredo who happily shows her his large record collection. He leaves her alone to leaf through his catalogue to pick out a record. Looking through the book she finds one record titled "The Last Scorpion". Pulling the record she finds the second red scorpion. Suddenly Alfredo appears with a gun demanding that she hand over the scorpion, telling her that Hans stayed with him before his death and suspected the scorpion was hidden in his home. Before Alfredo can take the scorpion he is shot dead by Freyda. However before Fredya can shoot the Blonde Phantom, Mark suddenly arrives and shoots her down as well. With the formula in US custody, the case is closed and Mark and Louise return home. On the flight, Mark brags about how exciting it was to work with the Blonde Phantom, much to Louise's chagrin.